實現 Trie (前綴樹)（LeetCode第208題）java實現

一、題目描述

實現一個 Trie (前綴樹)，包含 insert, search, 和 startsWith 這三個操作。

示例:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // 返回 true
trie.search("app");     // 返回 false
trie.startsWith("app"); // 返回 true
trie.insert("app");   
trie.search("app");     // 返回 true
說明:

你可以假設所有的輸入都是由小寫字母 a-z 構成的。
保證所有輸入均爲非空字符串。

二、解題思路

這是考察設計能力的題，在字節跳動面試題中出現過，難度爲中等，具體細節參考leetcode官網詳解：https://leetcode-cn.com/problems/implement-trie-prefix-tree/solution/shi-xian-trie-qian-zhui-shu-by-leetcode/

三、可運行java代碼

class TrieNode {

    private TrieNode[] links;

    private final int R = 26;

    private boolean isEnd;

    public TrieNode() {
        links = new TrieNode[R];
    }

    public boolean containsKey(char ch){
        return links[ch - 'a'] != null;
    }

    public TrieNode get(char ch){
        return links[ch - 'a'];
    }

    public void put(char ch, TrieNode node){
        links[ch - 'a'] = node;
    }

    public void setEnd(){
        isEnd = true;
    }

    public boolean isEnd(){
        return isEnd;
    }
}

//leetcode submit region begin(Prohibit modification and deletion)
class Trie {

   private TrieNode root;

    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            char currentChar = word.charAt(i);
            if(!node.containsKey(currentChar)){
                node.put(currentChar, new TrieNode());
            }
            node = node.get(currentChar);
        }
        node.setEnd();
    }

    public TrieNode searchPrefix(String word){
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            char curLetter = word.charAt(i);
            if (node.containsKey(curLetter)){
                node = node.get(curLetter);
            }else {
                return null;
            }
        }
        return node;
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node = searchPrefix(word);
        return node != null && node.isEnd();
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode node = searchPrefix(prefix);
        return node != null;
    }
}